1. Field of the Invention
This invention relates to pressure test and bypass valves used in well testing, and more particularly, to a combination pressure test and bypass valve which is pressure actuated in response to rupturing of a rupture disc.
2. Description of the Prior Art
Numerous well service operations entail running a packer into a well bore at the end of a string of tubing or drill pipe, and setting the packer to isolate a production formation or "zone" intersected by the well bore from the well bore annulus above the packer. After this isolation procedure, a substance such as a cement slurry, an acid or other fluid is pumped through the tubing or drill pipe under pressure and into the formation behind the well bore casing through perforations therethrough in an area below the packer. One major factor in insuring the success of such an operation is to have a pressure-tight string of tubing or drill pipe.
Another common well service operation in which it is desirable to assure the pressure integrity of the string of tubing or drill pipe is the so-called drill stem test. Briefly, in such a test, a testing string is lowered into the well to test the production capabilities of the hydrocarbon producing underground formations or zones intersected by the well bore. The testing is accomplished by lowering a string of pipe, generally drill pipe, into the well with a packer attached to the string at its lower end. Once the test string is lowered to the desired final position, the packer is set to seal off the annulus between the test string and the well casing, and the underground formation is allowed to produce oil or gas through the test string. As with the previously mentioned well service operations, it is desirable, prior to conducting a drill stem test, to be able to pressure test the string of drill pipe periodically to determine whether there is any leakage at the joints between the successive stands of pipe.
To accomplish this drill pipe pressure testing, the pipe string is filled with a fluid and the lowering of the pipe is periodically stopped. When the lowering of the pipe is stopped, the fluid in the string of drill pipe is pressurized to determine whether there are any leaks in the drill pipe above a point near the packer at the end of the string.
In the past, a number of devices have been used to test the pressure integrity of the pipe string. In some instances, a closed formation tester valve included in the string is used as the valve against which pressure thereabove in the testing string is applied. In other instances, a so-called tubing tester valve is employed in the string near the packer, and pressure is applied against the valve element in the tubing tester valve.
A problem with prior art pressure test/bypass valves is that the valve element therein may be operated prematurely when pulling out of the production packer. The present invention solves this problem by providing a tool which can be stung into and out of the production packer as many times as desired without prematurely opening the valve.